This invention generally relates to fluid conditioning apparatus and method and relates more particularly to improved techniques for inhibiting ice formation in such systems.
Fluid conditioning systems are utilized, by way of example, in aircraft to provide a conditioned airflow to the passenger or pilot cabins or to other locations in the aircraft requiring a controlled atmosphere. Typically such systems draw a pressurized source of air, either from the aircraft engine or other compressing source on board the aircraft for conditioning as to temperature and as to moisture content. Other functions accomplished by such a fluid conditioning system may include removal of contaminants or other undesirable elements in the airflow. In a closed system such as in an aircraft, tank or other occupied vehicle, system efficiency, weight, and simplicity become paramount designed considerations. Examples of such fluid conditioning systems may be found in U.S. Pat. Nos. 4,198,830 of Campbell, U.S. Pat. No. 3,452,273 of Kinsell et al, and U.S. Pat. Ser. No. 4,507,939 of Wieland having common assignee herewith.
For system efficiency and economy of weight it is typical in such fluid conditioning systems to utilize a turbine expander for heat removal from the airflow. Maximal efficiency is obtained by a large reduction in temperature of at least a portion of the airflow and subsequent mixing of the cold airflow with a warm airflow source. Higher system efficiencies in heat removal furthermore dictate higher pressure systems. High pressure systems such as described in the above referenced U.S. Pat. No. 4,507,939 typically include water condensation and moisture removal elements. However, even with utilization of such techniques the system is subject to ice formation under certain conditions of critical operation.
Previous anti-icing techniques for inhibiting a formation of ice within the system are inherent parasitic power losses reducing the overall system efficiency. Previous attempts to deal with this problem have been faced with the choice of either accepting a substantial parasitic power loss to maintain system simplicity, or introducing relatively complex, expensive and/or weight increasing elements and subsystems for controlling the anti-icing arrangement to minimize power consumption thereof.